The present invention relates to a semiconductor device and method of production thereof; and, more particularly, the invention relates to a semiconductor device which has a wiring structure made of copper, a basic wire protective film around said copper wiring, namely, covering the top of the copper wiring, and a barrier film surrounding the side and bottom of said copper wiring.
Improvement of the operation speed of a semiconductor device is required to achieve high integration and advanced operating capabilities. This requirement is accompanied by progress in miniaturization of LSI internal wiring and an increase in the number of layers. Miniaturization of wiring and an increase in the number of layers will cause the wiring resistance and the inter-wiring capacity to be increased and will affect the signal transfer speed in the wiring. Since an increase in the signal transfer speed is subjected to restrictions due to this delay time, the dielectric constant of the inter-layer insulation film is reduced to decrease the inter-wiring capacity. At the same time, the operation speed is improved by reducing the wiring resistance by use of a wiring material of lower resistance.
Therefore, studies have been made on the feasibility of using copper having a low specific resistance of 1.7 xcexcxcexa9cm as wiring material. As a technique to form copper wiring, the Dual Damasscene method is attracting attention. An example of this method will be described with reference to FIGS. 10(a) to 10(h).
FIG. 10(a) shows a substrate formed of a lower layer wiring layer 10a having a lower layer wiring 2b in this example and provided with wire protective film 8 characterized by high insulation on all sides. An insulation film 4 is formed on this substrate, as seen in FIG. 2(b), and a wiring groove 7 to embed wiring and a connection hole 10 to connect between upper and lower wiring are formed in said insulation film 4, as seen in FIG. 10(c). Since an insulating wire protective film 8 is located between the lower layer wiring layer 10a and the insulation film 4, the wire protective film 8 can be removed from the bottom of the connection hole 10. After barrier layer 3 has been formed on the surface of both the wiring grooves 7 and the connection hole 10, as seen in FIG. 10(d), a seed layer 5 is formed thereon, as seen in FIG. 10(e). Then, the wiring grooves 7 and the connection hole 10 are filled with wiring material 6, as seen in FIG. 10(f). Next, CMP (Chemical Mechanical Polishing) is used to remove the excess portion of the wiring material 6, and wiring plug 11 in the wiring 2 and connection hole 10 of the upper layer are formed simultaneously, as seen in FIG. 10(g). Then a wire protective film 8 is formed so as to cover the wiring 2 and insulation layer 4, as seen in FIG. 10(h). This Dual Damasscene method allows the wiring 2 and wiring plug 11 to be formed at one time, thereby ensuring a substantial reduction of the process cost.
Incidentally, copper reacts with insulation film 4 and is diffused in the insulation film. To ensure good wiring reliability, the insulating wire protective film 8 and barrier film 3 must be provided between the copper wiring 2 and the insulation film 4, as described above. Conventionally, a metal nitride, such as titanium nitride, tantalum nitride and tungsten nitride, which are capable of preventing copper diffusion, metals of high melting point, such as tantalum and tungsten and alloys thereof, have been used as a barrier film 3. In the meantime, an insulating silicon nitride film (SiN) has been used as the wire protective film 8 on the copper wiring 2.
However, SiN has a specific dielectric constant of 7.0 to 9.0. It has a dielectric constant twice that of an insulation film of SiO2, for example. Hence, it has been hindering reduction in the inter-wiring electric capacity in an extremely fine wiring pattern. To solve this problem, the electric capacity can be reduced by formation of a conductive film serving as a wire protective film on the top surface of the wiring.
U.S. Pat. No. 5,695,810 discloses that a cobalt-tungsten-phosphorus conducting film is formed by electroless plating as a wire protective film. In cobalt-tungsten-phosphorus electroless plating, sodium hypophosphite is commonly used as a reducing agent. Sodium hypophosphite is a known inert reducing agent without reaction occurring on copper which cannot be plated directly on copper (e.g. G. 0. Mallory, J. B. Hajdu, xe2x80x9cElectroless Platingxe2x80x94Fundamentals and Applicationsxe2x80x9d, American Electroplaters And Surface Finishers Society, Florida, Page 318, 1990). Hence, a cobalt-tungsten-phosphorus film must be formed by electroless plating after a seed layer, such as palladium, has been applied on the copper wiring. In this case, however, the palladium may react with the copper constituting the wiring layer to increase the copper resistance. Further, palladium may deposit on the insulation other than the wiring, so that a cobalt-tungsten-phosphorus film may be formed on the insulation other than wiring. Therefore, this involves a problem of reducing inter-wiring insulation required when producing fine wiring.
Furthermore, Japanese Official Patent Gazette 16906/1999 discloses the use of cobalt-containing electroless plating as an antioxidant film. However, the cobalt-containing film obtained from said method has an insufficient prevention capacity for a copper diffusion preventive film. If heat treatment is carried out in a semiconductor device forming process or after formation, copper diffuses into the SiO2 via the cobalt-containing film.
Japanese Official Patent Gazette 120674/1994 discloses that, in the production of the circuit substrate, an intermediate metallic film consisting of tungsten-cobalt-boron alloy as main component is formed on the surface of the wiring board provided with a wiring conductor and is coated with a circuit conductor composed of copper. However, the intermediate metallic film consisting of tungsten-cobalt-boron alloy as a main component is intended to increase the close adhesion between the wiring connector of tungsten or molybdenum on the circuit substrate surface and the circuit conductor of copper formed on the surface thereof; it does not function as a wire protective film between the copper wiring and insulation.
As described above, SiN which has been used as a wire protective film is an insulating material, and it has a high specific dielectric constant. It has been a factor hindering reduction of the inter-wiring electric capacity. To solve this problem, a wiring protective film can be formed with a metallic material allowing electric capacity to be reduced. However, metal nitrides, such as titanium nitride, tantalum nitride and tungsten nitride, which have been used as a wire protective film, and metals having a high melting point, such as tantalum and tungsten and alloys thereof, cannot be formed on the copper wiring alone on a selective basis. To avoid short circuiting between wires, such complicated processes as patterning and etching are required. This will cause deterioration in wiring formation accuracy and reliability. Thus, the following two issues must be solved in order to form a wire protective film with metallic materials:
(i) To ensure copper wiring reliability, it is necessary to form a metallic material capable of preventing copper diffusion without allowing the copper wiring to be oxidized in heat treatment.
(ii) Metallic material specified in (i) must be formed on the copper wiring alone on a selective basis.
A forming method meeting these two requirements must be provided. When a metal nitride, such as titanium nitride, tantalum nitride and tungsten nitride, or a metal having a high melting point, such as tantalum and tungsten or the alloy thereof, is used as a barrier film, a seed layer must be formed in order to provide copper plating because of high resistance. Especially, if the barrier film capable of working as a power feed layer can be formed, electric copper plating can be provided directly on the barrier film, and the conducting film (copper wiring film) can be formed effectively. Especially, when electroless plating is used to form a conductive barrier film, the barrier film can be formed uniformly despite a complicated configuration of wiring, and it works effectively as a seed layer of electric copper plating. However, a wire protective film or barrier film meeting these conditions has not been known up to the present time.
The object of the present invention is to solve the technical problems of the prior art. More specifically, the present invention is intended to prevent a rise in resistance due to oxidation of the copper wiring and reduction in the reliability of copper wiring and other elements due to copper diffusion. At the same time, it is intended to provide a semiconductor device and its forming method, wherein said semiconductor device is provided with a copper wire protective film and/or barrier film allowing uniform formation of a copper wiring film despite a complicated configuration.
To achieve the above object, the present invention provides a semiconductor device comprising a wire protective film to cover the top of the copper wiring formed in the insulation film and a barrier film surrounding the side and bottom of the copper wiring, wherein said wire protective film and/or barrier film is formed with a cobalt alloy film containing (1) cobalt, (2) at least one of chromium, molybdenum, tungsten, rhenium, thallium and phosphorus, and (3) boron.
The semiconductor device according to the present invention further characterized in that multiple layers of copper wires are formed in the insulation film, a wiring protective film and barrier film are covered with a cobalt alloy film containing (1) cobalt, (2) at least one of chromium, molybdenum, tungsten, rhenium, thallium and phosphorus, and (3) boron, and the copper wire on the upper layer is electrically connected with the copper wire on the lower layer through said barrier layer.
In another embodiment, the semiconductor device production method is characterized in that an insulation film serving as etching stop layer is further formed on the surface of the insulation film, except where the wire protective film is formed. The formation of such an etch stop layer on all surfaces facilitates the etching connection in the semiconductor device production process.
The present invention provides a semiconductor device production method characterized in that the semiconductor device comprises a wire protective film to cover the top of the copper wiring formed in the insulation film and a barrier film surrounding the side and bottom of the copper wiring; wherein said wire protective film and/or barrier film is formed with cobalt alloy film containing (1) cobalt, (2) at least one of chromium, molybdenum, tungsten, rhenium, thallium and phosphorus, and (3) boron.
The present invention prevents an increase in the resistance due to oxidation of the copper wiring and a reduction in the reliability of the copper wiring and other elements due to copper diffusion, and allows a wire protective film to be formed on the copper wiring alone on a selective basis. Since the barrier film is formed of said electroconducting cobalt alloy film, copper can be plated directly on the barrier film without requiring any power feed layer. This solves the problem of void formation and eliminates the step of forming a seed layer.
In the semiconductor device according to the present invention, said cobalt alloy, namely, wire protective film and/or barrier film, is preferred to have thickness of 100 nm or less and to contain 50 to 95 atomic percent cobalt as a main component, 1 to 40 atomic percent of at least one of chromium, molybdenum, tungsten, rhenium, thallium and phosphorus, and 0.1 to 10 atomic percent of boron.
The following describes the preferred embodiments of the semiconductor device and its production method according to the present invention with reference to drawings. The semiconductor device according to the present invention is basically manufactured according to the following process (See FIG. 1):
(a) A step, as seen in FIG. 1(b), of forming an insulation film 4 on the substrate 10a (not restricted to the lower layer copper wiring 2b and wire protective film 1a to be described later, which are already formed in FIG. 1(a) as an insulation layer;
(b) A step of forming a wiring groove 7 and connection hole 10 on the insulation film 4, as seen in FIG. 1(c);
(c) A step of forming a barrier film 3 on the surfaces in wiring groove 7 and connection hole 10, as seen in FIG. 1(d);
(d) A step of forming a seed layer 5 on the barrier film 4, as seen in FIG. 1(e);
(e) A step of embedding copper film 6 in the wiring groove 7 and hole 10, as seen in FIG. 1(f);
(f) A step of forming copper wiring 2 and wiring plug 11 by removing the copper 6 formed on the insulation film 4, other than in wiring groove 7 and hole 10, as seen in FIG. 1(g);
(g) A step of forming wire protective film 1 on the surface of copper wiring 2, as seen in FIG. 1 (h).
A semiconductor device with wiring layers laminated on the multilayer (four layers in the figure) is formed by repeating these steps (a) to (g) a required number of times as shown in FIG. 2.
The insulated material of SiO2, sylsesquioxane hydroxide and methyl siloxane, various materials of a low dielectric constant, and their laminated film can be used as insulation film 4. Copper wiring 2 can be formed by either electric copper plating or electroless copper plating. As will be described later, the step of forming the seed layer 5 can be eliminated and electroless copper plating of the copper wiring 2 can be facilitated when a cobalt alloy film according to the present invention is used as a barrier film 4.
A high melting point material, such as titanium, tantalum and tungsten or an alloy thereof, and a film nitride, such as titanium nitride, tantalum nitride and tungsten nitride, can be used as a barrier film 3. Further, a cobalt alloy film according to the present invention can also be used. In this case, the step of formation is enabled by immersing the substrate provided with wiring groove 7 and hole 10 into the cobalt based electroless plating bath.
The cobalt-based electroless plating bath contains a metal salt, a reducing agent, a completing agent, a pH regulator and an additive. Cobalt chloride, cobalt sulfide and cobalt nitrate can be used as the cobalt salt. As a tungsten salt, it is possible to use sodium tungstate, ammonium tungstate, ammonium trihydrate phosphotungstate, parapentahydrate anmnonium tungstate, sodium n-hydrate phosphotungstate, 12-tungstosilicic acid 26-water, tungstic acid, tungsten oxide, tungsten sodium citrate, tungsten disilicate, tungsten boride, etc. Sodium tungstate, ammonium tungstate, tungsten acid and tungsten sodium citrate are preferably used. As a molybdenum salt, it is possible to use molybdic acid, molybdenum chloride, potassium molybdate, disodium molybdate dihydrate, ammonium molybdate, silicide n-hydrate molybdate, molybdenum oxide acetylacetonato, sodium phosphomolybdate n-hydrate, molybdenum borate, etc. As a chromium salt, it is possible to use ammonium chromate, ammonium sulfate chromium dodecahydrate, chromium chloride hexahydrate, chromium sulfate, n-hydrate, chromium oxide, chromium borate, sodium dichromate dihydrate, etc. As a rhenium salt, it is possible to use ammonium perrhenate, potassium hexachlororhenate, etc. As a thallium salt, it is possible to use thallium nitrate, thallium formate, thallium sulfate, thallium oxide, etc. Phosphorus can be supplied from sodium phosphinate monohydrate, 3-aminopropyl phosphinic acid and phosphinic acid.
To form a wire protective film on the copper wiring 2 alone selectively, the reducing agent is hydrazine and a boron compound where the reaction proceeds on the surface of the copper wiring 2 and cobalt-plated film. It is also possible to use dimethyl amineborane, diethyl amineborane, amineborane, morpholine borane, pyridine borane, piperidine borane, ethylene diamine borane, ethylene diamine bis-borane, t-butyl amine borane, imidazol borane, methoxyethyl amine borane, sodium borohydride, etc. Use of such a reducing agent allows the wire protective film 1 to be formed directly on the copper wiring 2 without applying such a plating catalyst as palladium.
Citrate, succinate, malonate, malate, tartrate, etc. are preferred to be used as a completing agent. Alkali metal hydroxide such as sodium hydroxide, and potassium hydroxide, and organic alkali, such as ammonium, ammonium tetramethyl, ammonium tetraethyl, choline, etc. are preferred as a pH regulating alkali solution. A known surfactant, such as thiourea, saccharin, boric acid, thallium nitrate and polyethylene glycol, can be used as an additive. The temperature of the plating solution is preferred to be from 40 to 90xc2x0 C.
The wire protective film 1 formed by using this cobalt based electroless plating bath covers the top of the copper wiring 2 on an selective basis, as illustrated. Herein the wire protective film 1 exhibits an isotropic growth from the copper wiring 2, so that the film grows not only in the direction immediately above the copper wiring 2. It grows from the edge of the copper wiring 2 to the top of the barrier film 3 or insulation film 4 by a distance equivalent to the thickness of the wire protective film 1. When the wire protective film 1 is thinner than the barrier film 3, it grows to the top of the barrier film 3. If the wire protective film 1 is thicker than the barrier film 3, it expands to the top of the insulation film 4 over the barrier film 3. Further, if plating reaction in the surface of the barrier film 3 formed in step (c) is active, it is formed by extending beyond the top of the insulation film 4 isotropically from the edge of the barrier film 3, as shown in FIG. 3. Thus, due to isotropic growth of the wire protective film, the edge of the wire protective film 1 is round, not rectangular.
When the removed amount of the copper wiring 2 is greater than that of the barrier film 4 due to excessive polishing in the step (f), and the copper wiring 2 is more concave than the barrier film 4, namely, when so-called dishing has occurred, the cobalt based electroless plating solution is selected to ensure that deposition occurs only to the top of the copper wiring 2 without any deposition on the barrier film 4. Then, the concave portion of the copper wiring 2 can be reduced, and this is preferable.